The terrorist group Islamic State claims it carried out the truck attack at the Christmas market in Berlin in which 12 people were killed and 49 others injured.

The claim comes as German police hunt for the perpetrators after releasing a 23-year-old Pakistani man who was arrested near the scene of the Monday's attack minutes afterwards.

In a statement released through its "official" news channel, Amaq, Isis said: "The executor of the operation ... in Berlin is a soldier of the Islamic State." The statement continued: "He executed the operation in response to calls to target nationals of the coalition countries." The claims have not been independently verified, but claims issued via Amaq have some credibility.

Following the release of the only suspect, a 23-year-old Pakistani refugee known as Naved B, investigators are under huge pressure to locate the perpetrators.

It is thought the driver of the 25-tonne truck which mowed people down in the market also has a gun, as the Polish driver of the vehicle found dead in the cab, Lukasz Urban, had bullet wounds and stab wounds to his body.

The company which owns the lorry used in the attack - similar to the one in which 86 people died in Nice, France in July - has given investigators information about where it was parked in Berlin. Police are at the location, beside a canal in an industrial zone in the centre of the city.

Germany's Chancellor, Angela Merkel, has vowed to punish whoever is responsible "as harshly as the law requires." She is under increasing pressure as critics suggest her government's "open-door policy" has allowed terrorists to enter the country. However, investigators say it is too soon to tell what the motive was for the attack.

Berlin Gedaechniskirche truck attack 2016
A mourner lights candles at the Christmas market in Berlin, Germany, 20 December 2016 REUTERS/Hannibal Hanschke